Alkylation is the addition of an alkyl group to an organic molecule. In petroleum chemistry the process finds attractive utility in the reaction of an isoparaffin with an olefin molecule to yield an isoparaffin of higher molecular weight. Industrially, the concept depends on the reaction of a C.sub.2 -C.sub.5 olefin with isobutane in the presence of an acidic catalyst, producing the so-called alkylate. This is a very valuable ingredient in the manufacture of premium gasolines because of its high octane rating and good response to tetraethyl lead.
The catalysts employed in the industry are hydrofluoric acid or sulfuric acid carried out under controlled temperature conditions. Low temperatures are required in the sulfuric acid process to minimize the side reaction of olefin polymerization. The acid strength has to be maintained at 98-100 percent by the addition of fresh acid and the continuous withdrawal of spent acid.
The hydrofluoric acid process is less temperature-sensitive and the acid is easily recovered and purified. Any traces of water in the feedstock, however, have to be eliminated owing to the extreme corrosivity of hydrofluoric acid/water solutions.
These process materials and conditions are expensive and troublesome with problems such as maintaining an acid/hydrocarbon emulsion, careful temperature control with refrigeration, product separation and waste problems. Zeolites have been used, e.g. U.S. Pat. No. 3,251,902, to eliminate these problems with varying degrees of success. The catalysts found useful are rare-earth metal cation exchanged faujasite Y type zeolites (REHY). They appear to age rapidly and cannot perform effectively at high olefin space velocities.